The formation of foam in extracorporeal circulation circuits (E.C.C.'s) takes place mainly in the return from the surgical aspirators to the cardiotomy reservoir as a result of the forced blowing of air into the blood. It is thought that the formation of the foam is primarily caused by the high concentration of albumin, about 30 to 40 mg/ml, present in the blood. The foam formation occurs as a result of the agitation of the blood and air in the presence of albumin which acts as a stabilizing agent.
The destruction of foam in blood-treatment devices is currently carried out with the use of silicone compounds such as antifoaming compound A (Dow Coring), which is an emulsion of silicone oil and; silica.
Recent investigations of silicone oil, particularly for use in mammary prostheses, has caused a sensitization of public opinion with regard to the use of silicone in the biomedical field. Although no carcinogenic activity of silicone either in the form of oil or as a gel has been found, some effects on the immune system have been found. In particular, an adjuvant effect of silicone on the immune system has been found. See Chang, Plastic and Reconstructive Surgery, Vol. 92, No. 3, pp. 469-473 (1993); and Naim et al., Immunological Investigations, Vol. 22, No. 2, pp. 151-161 (1993).
The primary object of the present invention is to identify a method of reducing foam in blood which, while maintaining the foam-reducing performance achievable by the use of silicone antifoaming agents, does not involve the addition to the blood of agents which are not completely biocompatible or haemocompatible.
Foam-reducing methods based on physical-mechanical devices are known; these devices can be inserted directly in the venous reservoir and/or in the cardiotomy reservoir. Some examples are:
(a) micro-channels formed by machining on the surface of plastics materials such as, for example, Teflon, polycarbonate, Delrin, PVC; PA1 (b) filtering fabrics of Dacron and Teflon; PA1 (c) metal combs or machined steel and titanium surfaces; and PA1 (d) silicone elastomer coating of the polyurethane foam of the venous reservoir.
Chemical-physical destruction systems based on the use of antifoaming agents which can inhibit the formation of foam or can reduce the amount of foam without inhibiting its formation are also known.
Among the antifoaming agents, in addition to the antifoaming agent sold under the tradename compound A, already mentioned, surfactants belonging to the polyalkylene oxides class (such as the compounds sold under the tradename PLURONIC), amides and sulphonic compounds of long-chain alkenes, perfluoroethers and polyether polyols are known.
The article by Vardar-Sukan published in J. Chem. Tech. Biotechnol., Vol. 43, pp. 39-47 (1988) reports research relating to the effectiveness of natural oils as antifoaming agents in bioprocesses. In particular, in this article, the effectiveness of natural oils as antifoaming agents in substrates constituted by aqueous solutions of soya flour and sugar beet, which simulated fermentation media, was investigated. The effectiveness of various natural oils as antifoaming agents in these substrates was investigated, with the natural oils being added in concentrations variable between 0.2 and 1%. The conclusion was that effectiveness varies greatly in dependence on the substrate.
In view of the relatively high concentrations with which a satisfactory foam-suppression effect was achieved in the Vardar-Sukan article, it had to be considered that the use of these agents could not be contemplated for destroying foam in blood because, in this case, the release of the agent into the blood necessarily has to be kept to minimal levels.
Surprisingly, as a result of the present invention, it has been found that fatty acid triglycerides have a suppressant effect on foam in the blood and its derivatives equivalent to that of the conventional antifoaming agents used for this purpose when they are impregnated or bound to a contact-generating substrate which contacts a blood substance.